Theater dimmer control



y 1936. D.- D. KNOWLES 6,

THEATER DIMMER CONTROL Filed Dec. 14, 1934 7W BY ATTORNEY Patented July 7, 1936 'UNITED STATES PATENT OFFlfiE' DIMMEB CONTROL Pennsylvania Application December 14, 1934, Serial No. 157,560

1 Claims. (or. 175-312) My invention relates to translating apparatus .and has particular relation to apparatus for controlling and varying illumination, such as the stage and auditorium lights of a theater.

In accordance with the practice of the prior art, of which I am aware, the illumination in theatres and other public institutions is continuously varied from its maximum value to darkness by varying the reactance of an inductor in series with the illuminating units and a power source. The inductor is provided with an auxiliary or input winding through which direct current is transmitted to vary the reactance. In apparatus constructed in accordance with the teaching of the prior art, the direct current is supplied through gas-filled discharge devices of the hot-cathode type. Each discharge device is provided with a control electrode and a plurality of principal electrodes, and to vary the reactance, the control potential (i. e., the potential impressed between the control electrode and one of the principal electrodes, preferably the cathode) is shifted in phase relative to the. principal potential, (i. e., the potential impressed between the principal electrodes). The necessity for phase-shift arises from the fact that the discharge device has anabrupt characteristic and its output current varies discontinuously.

While apparatus of the general type discussed above has been used with considerable success in the past, it has several disadvantages. The hotcathode discharge devices cannot be so constructed as to become immediately energized when power is supplied to thersystem. Hence either the cathodes of the discharge devices used must be maintained continuously in energized condition, or the operation of the system must be delayed for several minutes after the power turned on during any performance. As to the former of these-alternatives, it is to be remembered that the lighting control system for a theater of moderate size involves several hundred units, each incorporating several electric discharge devices. Consequently, the loss of power engendered by maintaining the cathodes continuously heated is considerable. On the other hand, in the theater industry where the most elaborate care is taken to carry out every detail to the greatest perfection, apparatus, in which a delay of several minutes is involved, is a highly disturbing factor.

The apparatus of the prior art has another disadvantage. The equipment for shifting the phase of the control and principal potentials of the discharge device in general involves a 'network incorporating an inductor, or a capacitor, and a resistor, one or both of the elements being variable. capacity, the reactor and resistor required are For a discharge device of moderate electric discharge device having an abruptcharacteristic, in which the output of the discharge device shall be varied without the use of the conventional phase shifting elements.

An incidental object of my invention is to provlde translating apparatus for supplying variable current of the type incorporating an electric discharge device having an abrupt characteristic, in which the current output of the discharge device shall be capable of variation without the use of the conventional phase shifting elements.

More concisely stated,-it is an object of my invention to provide apparatus for controlling and varying illumination, such as a system of theater lights that shall be compact and inexpensive, and that shall functionwith facility.

According to my invention, -1 provide apparatus. incorporating an Ignitron discharge device. The discharge device incorporates an anode and a cathode preferably of mercury in which an electrode of carborundum or boron carbide is immersed. The carborundum electrode and the mercury electrode constitute starting or initiating electrodes. When current is transmitted between the initiating electrodes a discharge is initiated between the anode and the cathode. The anode and cathode are connected to supply current to the input windings of a reactor, and when the discharge is initiated the reactance of the reactor is varied.

The initiating current is supplied through a grid controlled electric discharge device of the high-vacuum type. The latter has a continuous characteristic and becomes immediately operable when energy is supplied thereto. The

.current output of the high vacuum device is varied by varying the magnitude of the control potential relative to the principal potential. As

the output of the high-vacuum device is varied, the point in the half cycles of principal potential at which the discharge in the Ignitron tube is initiated is varied and thus the reactance of the inductor is varied.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with additional objects and advantages thereof will best be understood from the following description of a specific embodiment when read in connection with the accompanying drawing, in which:

Figure 1 is a diagrammatic view showing a preferred embodiment of my invention; and

Fig. 2 is a graph illustrating the operation of Fig. 1.

The apparatus shown in the drawing comprises an illuminating system I which may be symbolical of the lights in a theater, or in any other public institution. The illuminating system I is supplied with power from a power source 2 through the output windings 3 of a reactor 5. The input windings I of the reactor are supplied with current from an alternatingcurrent source 8 through an Ignitron electric discharge device 9. The discharge device 9 incorporates an anode II- of nickel, iron or carbon or any other suitable metal, a cathode I3 preferably of mercury, although other metals might be utilized, and an electrode I5 preferably of boron carbide immersed in the mercury electrode I3. A discharge is initiated between the anode I I and the cathode I3 by the transmission of a pulse of current through the mercury I3 and the electrode I5. It is apparent that while for convenience the electrode I3 serves the double function of initiating electrode and cathode a separate electrode may be provided for this purpose.

The initiating current is supplied through a spark tube I I. The latter comprises a plurality of solid electrodes I9 and 2I immersed in a gaseous atmosphere at a pressure of the order of several centimeters of mercury. One electrode I9 of the spark tube I I is connected to the initiating electrode I5. A capacitor 23 is connected between the mercury electrode I3 and the other electrode 2| of the spark tube II.

The capacitor 23 is charged through an electric discharge device 25 of the high vacuum type, which may be supplied with potential from a separate alternating power source 26. The high-vacuum discharge device 25 comprises an anode 21, a hot cathode 29 and a control electrode 3|. The hot cathode 29 is of the directly -heated type, and the discharge device 25 becomes immediately operative when supplied with potential.

To vary the charging current, a potentiometer 33 is provided. The movable tap 35 of the potentiometer is connectedto the control electrode 3I, while its upper terminal 31 is connected to the cathode 29. 'As the position of the movable tap 35 of the potentiometer 33 is varied, the magnitude of the control potential of the high-vacuum discharge device 25 is varied and consequentlyits current output is varied.

The principal electrodes 21 and 29 of the discharge device 25 are connected in series circuit with a secondary section 39 of a power supply transformer 4| and the capacitor 23. As the output of the high-vacuum discharge device 25 is varied the rate of charging of the capacitor 23 is varied. As the capacitor 23 charges, the

' difference of potential impressed between the electrodes I9 and 2| of the spark tube I1 is varied, and when it attains a predetermined value, the spark tube breaks down, a current is transmitted between the initiating electrodes I3 and I5 and a discharge is initiated between the anode 'II and the cathode I3 of the main discharge device 9. As the discharge current is now transmitted through. the input windings i of the reactor 5, the reactance is decreased to an extent dependent upon the magnitude of the current and, the drop in potential across the illumination I being increased, the luminous output is also increased.

The operation of the system is illustrated in Fig. 2, in which the full-line curve 43 represents a positive half cycle of principle potential supplied to the main discharge device 9, while the broken-line curve 45 represents a half cycle of principal potential supplied to the series net- 1 work including the high-vacuum discharge device 25 and the capacitor 23. The straight line 41 above the axis of abscissa 49 represents the potential at which the spark tube I I becomes energized. 1,

The rapidity with which the difference of potential impressed on the capacitor 23 rises to the breakdown value of the spark tube l'I depends on the control potential supplied to the high vacuum discharge device 25. As the control po- 2 tential is varied, the rate of charging may be varied over a wide range, and the point in the half cycle of principal potential at which the spark tube I1 becomes energized may be varied. The main discharge device 9 only becomes ener- 2 gized at the instant that the spark tube I1 is energized, and, consequently, the point in the half cycle of principal potential at which the main discharge device becomes energized is varied, as the control potential of the high vac- 3 guum discharge device is varied. Since the main .discharge device 9 when once energized continues to supply current during the remaining portion of the positive half-cycle of principal potential regardless of whether or not initiating current is supplied, the current supplied to the input winding I of the reactor 5 may be varied by varying the point in the half cycle of positive principal potential at which the discharge is initiated. Thus, for one value of control poten- 4 tial the difference of potential impressed on the capacitor 23 rises along the curve 5I while for another it rises along the curve 53. In the former case the discharge current will be supplied to the input winding during an interval of time 4 represented by the portion of the abscissa lying between the line 55 and the end of the half-cycle '51 while in the latter case the corresponding interval of time will be represented by the portion between the line 59 and the point 51. The 5 current supplied in the former case will be greater than the current supplied in the latter case.

By sliding the movable tap of the potentiometer back and forth, the output of the illumina- 5 tion may thus be adjusted and continuously varied. Since the response of the main discharge device to starting current is immediate, no time delay element is involved.

Although I have shown and described a cer- 61 tain specific embodiment of my invention, I am fully aware that many modifications thereof are possible. My invention, therefore, is not to be restricted, except insofar as is necessitated by the prior art and by the spirit of the appended 0: claims.

I claim as my invention:

1. Apparatus for continuously varying the light output of a system of lighting units comprising a power source, a reactor having input 7 and output windings, means for connecting said output windings to said lighting units and said source whereby said lighting units are energized through said output windings, an electric discharge device having a plurality of principal 7:

source whereby said lighting units are enerelectrodes between which a discharge current is to pass and a plurality of initiating electrodes between which a current is to be transmitted to initiate said discharge, means for supplying current between said initiating electrodes, said means including a capacitor, means for charging said capacitor and means for discharging said capacitor through said initiating electrodes when it has been charged to a predetermined difierence of potential.

2. Apparatus for continuously varying the light output of a system of lighting units comprising a power source, a reactor having input and output windings, means for connecting said output windings to said lighting units' and said source whereby said lighting units are energized through said output windings, an electric discharge device having a plurality of principal electrodes between which a discharge current is to pass and a plurality of initiating electrodes between which a current is to be transmitted to initiate said discharge, means for supplying current between said initiating electrodes, said means including a capacitor, -means incorporating an electric discharge device having a control electrode and a plurality of principal electrodes, means for impressing potentials between said control electrode and said principal electrodes, and means for varying the magnitude only of the potential impressed between said control electrode and said principal electrodes.

3. In combination an electric discharge device comprising a plurality of principal electrodes between which a discharge is to pass and a plurality of initiating electrodes between whicha current is to be transmitted to initiate said discharge, means for impressing aperiodic potential between said principal electrodes, chargestoring means, means for charging said chargestoring means, means for discharging said charge-storing means between said initiating electrodes to initiate the discharge between said principal electrodes, said charging means including means for varying the rate of charging, whereby the point in the periods of said periodic potential at which said discharge is initiated is varied.

4. In combination an electric discharge device comprising a plurality of principal electrodes between which a discharge is to pass and a plural ity of initiating electrodes between which a current is to be transmitted to initiate said discharge, means for impressing a periodic potential between said principal electrodes, chargestoring means, means for charging said chargestoring means, means for discharging said charge-storing means between said initiating electodes to initiate the discharge between said principal electrodes, said charging means including an electric discharge device having a control electrode and a plurality of principal electrodes, means for impressing potentials between said control electrode and said principal electrodes and means for varying the magnitude only of the last said potentials to vary the rate of charging, whereby the point in the periods of said periodic potential at which said discharge is initiated is varied.

5. Apparatus for continuously varying the light output of a system of lighting units comprising a periodic power source, a reactor having input and output windings, means for connecting said output windings to said lighting units and said gized through .said output windings, an electric discharge device having a plurality of principal electrodes between which a discharge current is to pass and a plurality of initiating electrodes between which a current is to be transmitted to initiate said discharge, said discharge device being of the type wherein the principal electrodes are normally cold and the discharge, when it is initiated, passes between a cathode spot on one principal electrode and another principal electrode, means for transmitting an impulse of current sufllcient to initiate a discharge between said principal electrode, said impulse persisting for less than a period of said source and means for connecting said principal electrodes to said input windings in such manner that the current of said discharge is transmitted through said windings.

6. Apparatus for continuously varying the light output of a system of lighting units comprising a periodic power source, a reactor having input and output windings, means for connecting said output windings to said lighting-units and said source whereby said lighting units are energized through said output windings, an electric discharge device having a plurality of principal electrodes between which a discharge current is to pass and a plurality of initiating electrodes between which a current is to be transmitted to initiate said discharge, said discharge device being of the type wherein the principal electrodes are normally cold and the discharge, when it is initiated, passes between a cathode spot on one principal electrode and'another principal electrode, and means including a high vacuum discharge device of the type that has the property of asymmetric conductivity and that becomes immediately completely operative when power is supplied thereto for transmitting a pulse of current for an interval of time smaller than a period of said source between said initiating electrodes to initiate the discharge.

7. Apparatus for continuously varying the light 'output of a system of lighting units comprising a periodic power source, a reactor having input and output windings, means for connecting said output windings to said lighting units and said source whereby said lighting units are energized through said output windings, an electric discharge device having a plurality of principal electrodes between which a discharge current is to pass and a plurality of initiating electrodes between which a current is to be transmitted to initiate said discharge, means for transmitting a current between said initiating electrodes to initiate a discharge between said principal electrodes, the last said means including an element and means for applying a potential to said element, said element operating to prevent the passage of said starting current when said potential is below a predetermined value and to abruptly permit the passage of a pulse of current, sufllcient to start a discharge between said principal electrode, when saidpotential is above said value,

said pulse persisting for less than a period of said source, means for connecting said principal electrodes to said input windings in such manner that the current of said discharge is transmitted through said windings and means for varying the potential applied to said element to vary the magnitude of the current of said discharge.

DEWEY D. KNOWLES. 

